This invention relates to apparatus for detecting magnetic phenomena and is more particularly concerned with a magnetic locator and a method of manufacturing the same.
Devices for locating magnetic objects and/or for detecting or measuring magnetic fields are well known. Such devices may comprise a plurality of magnetic sensor units, including appropriate windings or coils, which are spaced apart and mounted within a non-magnetic tubular housing. See, for example, U.S. Pat. Nos. 3,281,660; 2,642,479; 2,620,381; and 3,064,185. The applicant himself has disclosed such devices and various types of sensors which may be used therein. See, for example, U.S. Pat. Nos. 3,050,679; 3,487,459; 3,488,579; 2,916,696; 2,981,885; 3,168,696; 3,076,930; 3,426,269; and 3,439,264. In general, prior magnetic detecting apparatus employing a pair of spaced magnetic sensors in a tubular housing has suffered from one or more of the following deficiencies: complexity, high cost, poor sensitivity. Prior electrical circuits for use in magnetic locators, such as those disclosed in patents cited above, or those disclosed in U.S. Pat. Nos. 3,274,488; 3,461,387; 3,355,658, tend to be unduly complex and expensive. A prior art magnetic locator sold commercially by the applicant's assignee is indicative of the complexity and expense of prior devices. In that locator the sensor cores are individually wound with multiple turns of thin excitation wire and placed in a tube upon which signal windings are wound. This assembly is placed in another tube which is attached to the end of a further tube. The circuit includes synchronous detectors and a voltage to frequency converter.